The present invention relates to a pneumatic tire, more specifically, to a pneumatic tire arranged to enhance on-ice performances on snowy and icy roads without degrading driving stability as on dry roads and to suppress occurrence of uneven wear thereof.
Generally, a pneumatic tire to be used on snowy and icy roads has a constitution that multiple blocks are partitioned and formed on a tread face by main grooves extending in a circumferential direction of the tire and by sub grooves extending in a width direction of the tire, in which multiple sipes are further provided on treads of the blocks. The pneumatic tire is designed to secure driving and braking performances on snowy and icy roads (hereinafter referred to as “on-ice performances”) owing to scratching actions onto the snowy and icy roads by edges at both front and back ends of these blocks as well as edges of the sipes (such actions will be hereinafter referred to as an “edge effect”).
If the number of the sipes is increased in order to further enhance the on-ice performances of the above-described pneumatic tire, contactability of the tire is degraded because shear rigidity of the blocks are reduced. Accordingly, such an increase in the number of sipes cannot enhance the on-ice performances significantly, and, if anything, uneven wear tends to be more prominent by the increase. Various modes have been proposed in the past as countermeasures for the foregoing problems. The countermeasures proposed in the past attempted to enhance the shear rigidity of the blocks by forming wall surfaces of the sipes into concave and convex shapes so that the wall surfaces are engaged with one another, or by reducing widths (or thicknesses) of the sipes.
However, those countermeasures by means of increasing engagement between the concave and convex shapes of the wall surfaces of the sipes or reducing the widths (or thicknesses) of the sipes had problems such as degradation of releaseability upon releasing a tire from a mold after curing, or breakage of sipe-forming blades due to lack of strength caused by thinning.